Induction of diapause egg production in Eurytemora affinis by their own metabolites

Chemically mediated crowding effect on induction of diapause egg production in the calanoid copepod Eurytemora affinis was investigated. Two types of eggs, i.e. subitaneous and diapause eggs, produced by females that were reared in crowded culture conditions or the water from crowded culture under excess food supply were examined. 2.3% of the females that were reared at a population density of 5 or 6 animals per 10 ml of filtered lake water (FLW) produced diapause eggs. Females that were reared individually in 2-ml containers with FLW did not produce diapause eggs while 72.7% of females that were individually reared in 2-ml containers, but with water from a crowded culture (500 ind. l^–1, culture medium was changed once a week), produced diapause eggs. These results demonstrate that accumulation of their own metabolic products in the medium induces diapause egg production by E. affinis.